this subject is too subjective to be solved, but...my point of view...

USA
~Elvis
~Jimmi Hendrix
~Jim Morrison (The Doors)

UK
~The Beatles
~Pink Floyd
~Led Zeppelin

In my opinion, the US contributed to revolutionary rock individuals and the UK gave us revolutionary bands. So I would have to say that they're equals in contribution....and they all bow down to Canada!!! The Guess Who, BTO, Rush, Neil Young, Kim Mitchell, Bryan Adams, April Wine, Trooper, Steppen Wolf, The Hip ....you Yankee's and Brits have nothing on us Canucks.